Silicon Carbide Device with Compensation Layer and Method of Manufacturing

ABSTRACT

First dopants are implanted through a larger opening of a first process mask into a silicon carbide body, wherein the larger opening exposes a first surface section of the silicon carbide body. A trench is formed in the silicon carbide body in a second surface section exposed by a smaller opening in a second process mask. The second surface section is a sub-section of the first surface section. The larger opening and the smaller opening are formed self-aligned to each other. At least part of the implanted first dopants form at least one compensation layer portion extending parallel to a trench sidewall.

TECHNICAL FIELD

Examples of the present disclosure relate to a silicon carbide device,in particular to a silicon carbide device with compensation layer and tomethods of manufacturing silicon carbide devices with compensationlayer.

BACKGROUND

The most significant difference between conventional power semiconductordevices and power semiconductor superjunction power devices is a seriesof lateral junctions between n doped regions and p doped regions in thevoltage-sustaining layer of the superjunction power semiconductordevice. A lateral depletion effect inside the voltage sustaining layerfacilitates high voltage blocking capability at comparatively lowon-state resistance. A prerequisite for high voltage blocking capabilityis sufficient charge balance between the n doped regions and the p dopedregions in the voltage-sustaining layer. Fabrication of siliconsuperjunction devices typically includes a multi-epitaxy/multi-implantprocess with masked p-type doping or with both masked p-type and maskedn-type doping per epitaxial layer, a multi-implant process at differentimplant energies, etching trenches combined with epitaxial growth in thetrench, or etching trenches combined with a trench-wall gas-phase dopingprocess. Forming compensation structures with high vertical extensionand with sufficiently well-defined charge compensation gets morechallenging if the diffusion coefficient of dopants in the semiconductormaterial is low.

There is a need for providing a silicon carbide device including acompensation structure with high vertical extension and/or well-definedcharge compensation at competitive costs.

SUMMARY

An embodiment of the present disclosure relates to a method ofmanufacturing a silicon carbide device. First dopants are implanted intoa silicon carbide body through a larger opening of a first process mask.The larger opening exposes a first surface section of the siliconcarbide body. A trench is formed in the silicon carbide body in a secondsurface section exposed by a smaller opening in a second process mask.The second surface section is a sub-section of the first surfacesection. The larger opening and the smaller opening are formedself-aligned to each other. At least part of the implanted first dopantsform at least one compensation layer portion extending parallel to atrench sidewall.

Another embodiment of the present disclosure relates to a siliconcarbide device. The silicon carbide device includes a fill structureextending from a first lateral cross-sectional plane of a siliconcarbide body to a second lateral cross-sectional plane. The fillstructure includes at least one stepped sidewall. The stepped sidewallincludes at least two steep sidewall portions laterally shifted to eachother. Compensation layer portions are formed in the silicon carbidebody. Each compensation layer portion extends along one of the steepsidewall portions.

Those skilled in the art will recognize additional features andadvantages upon reading the following detailed description and onviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the embodiments and are incorporated in and constitutea part of this specification. The drawings illustrate embodiments of asilicon carbide device and a method of manufacturing a silicon carbidedevice and together with the description serve to explain principles ofthe embodiments. Further embodiments are described in the followingdetailed description and the claims.

FIGS. 1A-1B show simplified vertical cross-sectional views of a portionof a silicon carbide body for illustrating a method of forming a siliconcarbide device with compensation structure according to an embodimentincluding etching a trench into a doped auxiliary region.

FIGS. 2A-2B show simplified vertical cross-sectional views of a portionof a silicon carbide body for illustrating a method of forming a siliconcarbide device with compensation structure according to an embodimentincluding a vertical implant in sidewall regions of a trench.

FIGS. 3A-3N show simplified vertical cross-sectional views of a portionof a silicon carbide body for illustrating a method of forming a siliconcarbide device witch trench gate structures according to an embodimentusing spacers.

FIGS. 4A-4D show simplified vertical cross-sectional views of a portionof a silicon carbide body according to an embodiment providingcompensation adjustment regions.

FIGS. 5A-5C show simplified vertical cross-sectional views of a portionof a silicon carbide body for illustrating a method of forming a siliconcarbide device according to an embodiment including ion implantationafter forming a trench with stepped trench sidewalls.

FIG. 5D show a simplified vertical cross-sectional view of a portion ofa silicon carbide body for illustrating a method of forming a siliconcarbide device according to an embodiment providing self-aligned gatetrenches.

FIGS. 6A-6B show simplified vertical cross-sectional views of a portionof a silicon carbide body according to an embodiment providingcompensation connection regions.

FIGS. 7-9 illustrate schematic vertical cross-sectional views ofportions of silicon carbide devices with compensation structuresincluding laterally shifted steep compensation layer portions accordingto embodiments concerning transistor cells with trench gate structuresand one-sided channels.

FIG. 10 illustrates a schematic vertical cross-sectional view of aportion of a silicon carbide device with a compensation structureincluding laterally shifted steep compensation layer portions accordingto an embodiment concerning transistor cells with planar gatestructures.

FIGS. 11A-11B are schematic lateral and vertical cross-sectional viewsof a portion of a SiC SJ-TMOSFET (silicon carbide superjunction trenchmetal oxide semiconductor field effect transistor) with two-sidedchannel according to an embodiment.

FIGS. 12A-12B are schematic lateral and vertical cross-sectional viewsof a portion of a SiC SJ-TMOSFET with two-sided channel according toanother embodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof and in which are shownby way of illustrations specific embodiments in which a silicon carbidedevice and a method of manufacturing a silicon carbide device may bepracticed. It is to be understood that other embodiments may be utilizedand structural or logical changes may be made without departing from thescope of the present disclosure. For example, features illustrated ordescribed for one embodiment can be used on or in conjunction with otherembodiments to yield yet a further embodiment. It is intended that thepresent disclosure includes such modifications and variations. Theexamples are described using specific language, which should not beconstrued as limiting the scope of the appending claims. The drawingsare not scaled and are for illustrative purposes only. Correspondingelements are designated by the same reference signs in the differentdrawings if not stated otherwise.

The terms “having”, “containing”, “including”, “comprising” and the likeare open, and the terms indicate the presence of stated structures,elements or features but do not preclude the presence of additionalelements or features. The articles “a”, “an” and “the” are intended toinclude the plural as well as the singular, unless the context clearlyindicates otherwise.

The term “electrically connected” describes a permanent low-resistiveconnection between electrically connected elements, for example a directcontact between the concerned elements or a low-resistive connection viaa metal and/or heavily doped semiconductor material. The term“electrically coupled” includes that one or more intervening element(s)adapted for signal and/or power transmission may be connected betweenthe electrically coupled elements, for example, elements that arecontrollable to temporarily provide a low-resistive connection in afirst state and a high-resistive electric decoupling in a second state.An “ohmic contact” is a non-rectifying electrical junction with a linearor almost linear current-voltage characteristic.

The Figures illustrate relative doping concentrations by indicating “−”or “+” next to the doping type “n” or “p”. For example, “n-” means adoping concentration which is lower than the doping concentration of an“n”-doping region while an “n+”-doping region has a higher dopingconcentration than an “n”-doping region. Doping regions of the samerelative doping concentration do not necessarily have the same absolutedoping concentration. For example, two different “n”-doping regions mayhave the same or different absolute doping concentrations.

Two adjoining doping regions of the same conductivity type and withdifferent dopant concentrations form a unipolar junction, e.g., an n/n+or p/p+ junction along a boundary surface between the two dopingregions. At the unipolar junction a dopant concentration profileorthogonal to the unipolar junction may show a step or a turning point,at which the dopant concentration profile changes from being concave toconvex, or vice versa.

A charge compensating layer is a layer that at least partly compensatesthe charge in an adjacent complementarily doped layer or region whenboth layers are depleted or partly depleted. For example, the integralof the doping density along a lateral line across the chargecompensating layer and the adjacent complementarily doped layer orregion may be in a range from −20% to +20% of the integral of the dopingalong a lateral line across the more heavily doped one of the chargecompensating layer and the complementarily doped layer or region. Thecharge compensating layer is completely depleted at least at the typicaldevice breakthrough voltage or at a lower blocking voltage.

A charge compensating layer and one or two adjacent complementarilydoped layer(s) or region(s) exhibiting the defined degree of chargecompensation may form a unit cell of a compensation structure. Thecharge compensating layer is referred to as “compensation layer” in thefollowing for simplicity. A section of a charge compensating layer isreferred to as “compensation layer portion” in the following.

Ranges given for physical dimensions include the boundary values. Forexample, a range for a parameter y from a to b reads as a≤y≤b. The sameholds for ranges with one boundary value like “at most” and “at least”.

Main constituents of a layer or a structure from a chemical compound oralloy are such elements which atoms form the chemical compound or alloy.For example, nickel and silicon are the main constituents of a nickelsilicide layer and copper and aluminum are the main constituents of acopper aluminum alloy.

The term “on” is not to be construed as meaning “directly on”. Rather,if one element is positioned “on” another element (e.g., a layer is “on”another layer or “on” a substrate), a further component (e.g., a furtherlayer) may be positioned between the two elements (e.g., a further layermay be positioned between a layer and a substrate if the layer is “on”said substrate).

As regards structures and doped regions formed in a silicon carbidebody, a second region is “below” a first region if a minimum distancebetween the second region and a first surface at the front side of thesilicon carbide body is greater than a maximum distance between thefirst region and the first surface. The second region is “directlybelow” the first region, where the vertical projections of the first andsecond regions into the first surface overlap. The vertical projectionis a projection orthogonal to the first surface.

The term “power semiconductor device” refers to semiconductor deviceswith high voltage blocking capability of at least 30 V, for example 100V, 600 V, 3.3 kV or more and with a nominal on-state current or forwardcurrent of at least 1 A, for example 10 A or more.

In general, a “layer” exhibits a surface extension along two orthogonaldirections and an approximately uniform layer thickness orthogonal tothe surface extension. The layer thickness may be smaller than, e.g., atmost 10% of, the smallest linear extension along the surface extension.The surface extension of a lateral layer is parallel to a lateral plane.A layer extending parallel to a trench sidewall has a surface extensionparallel to the trench sidewall and may have an approximately uniformthickness in a direction orthogonal to the trench sidewall.

According to an embodiment, a method of manufacturing a silicon carbidedevice may include implanting first dopants through a larger opening ofa first process mask into a silicon carbide body.

The silicon carbide body may be one of several silicon carbide bodiesarranged side-by-side and laterally connected to each other. Thelaterally connected silicon carbide bodies may be portions of a siliconcarbide substrate.

The silicon carbide substrate may consist of or include a siliconcarbide disc or silicon carbide wafer cut from a single-crystallinesilicon carbide ingot. For example, the silicon carbide substrate mayinclude an epitaxial layer and/or a substrate portion, wherein thesubstrate portion may be obtained from a single-crystalline siliconcarbide ingot, e.g. by sawing or wafer splitting. A diameter of thesilicon carbide substrate may correspond to a production standard forsemiconductor wafers, and may be, by way of example, 4 inch (100 mm),150 mm (6 inch), 175 mm (7 inch), 200 mm (8 inch) or even up to 300 mm(12 inch).

The material of the silicon carbide substrate may be 15R—SiC (siliconcarbide of 15R polytype), 2H—SiC, 4H—SiC or 6H—SiC, by way of example.In addition to the main constituents silicon and carbon, the siliconcarbide substrate may include dopant atoms, for example nitrogen N,phosphorus P, beryllium Be, boron B, aluminum Al, and/or gallium Ga.Further, the silicon carbide substrate may include unwanted impurities,for example hydrogen, fluorine and/or oxygen.

The silicon carbide substrate may have two essentially parallel mainsurfaces of the same shape and size and a lateral surface areaconnecting the edges of the two main surfaces. For example, the siliconcarbide substrate may have the shape of a polygonal (e.g., rectangularor hexagonal) prism with or without rounded edges, a right cylinder or aslightly oblique cylinder, wherein some of the sides may lean at anangle of at most 8°, at most 5° or at most 3°. One or more flats ornotches may be formed along the lateral surface area.

The silicon carbide substrate may laterally extend in a plane spanned bylateral directions. Accordingly, the silicon carbide body may have asurface extension along two lateral directions and may have a thicknessalong a vertical direction perpendicular to the lateral directions. Afirst surface of the silicon carbide body forms a section of a firstmain surface at the front side of the silicon carbide substrate.

The first process mask may be a homogeneous layer from one material ormay include two or more sub-layers of different materials. For example,the first process mask may include a layer of silicon oxide and/or alayer of silicon nitride. The first process mask may be formed on, e.g.directly on, the first surface of the silicon carbide body.

The larger opening may extend vertically through the first process mask.The larger opening may expose a first surface section of the firstsurface. The first surface section may be planar or may include atrench. The larger opening may be stripe-shaped. Alternatively, thelarger opening may be a regular polygon with or without rounded orbeveled corners, a circle, or an oval, by way of example.

The first dopants may be implanted into an implant region in a way suchthat a distribution of the implanted first dopants along the verticaldirection is uniform to a high degree, e.g. over at least 50% or even atleast 70% or even at least 80% of the vertical extension of the implantregion. In other words, a vertical dopant distribution in thecompensation layer portion may be approximately uniform (so-called“box-shaped” distribution), e.g. over at least 50% (or 70% or 80%) ofthe vertical extension of the implant region. For example, implantingthe first dopants may include a high energy implant through an energyfilter. The implanted dopants may have an approximately uniform energydistribution between a minimum energy and a maximum energy and/or theimplanted dopants distribute approximately uniformly along the verticaldirection. According to other embodiments, implanting the first dopantsmay include at least one of: (i) channeled ion beam implantation, (ii)ion beam implantation at a plurality of different acceleration voltages,(iii) ion beam implantation at a plurality of different implant angles.With each of these methods, it may be possible to approximate abox-shaped vertical dopant profile to some degree. A verticalhomogeneous doping level may mean that the difference in the dopinglevel in this region is less than 60% or less than 40% or even less than20% of a maximum doping level in this region.

Prior to or subsequent to implanting the first dopants, a trench may beformed in a second surface section of the first surface of the siliconcarbide body. The trench may be circle shaped, polygon shaped or stripeshaped and may laterally extend from one side of a central active regionof the silicon carbide body to the opposite side. The central activeregion may include functional transistor cells of a power semiconductordevice, or the anode region(s) of a power semiconductor diode or MPS(merged pin Schottky) diode.

Alternatively, the trench may be a needle trench with two orthogonallateral extensions within the same order of magnitude. For example, aneedle trench may have two equal or approximately equal orthogonallateral extensions. The trench may have at least one steep trenchsidewall. For example, the trench sidewall may include one, two or moresteep sidewall sections. The steep sidewall sections may be vertical ormay deviate from the vertical direction by up to ±10 degree, by way ofexample.

The second surface section may be exposed by a smaller opening in asecond process mask. The second surface section may be a truesub-section of the first surface section. In other words, a lateral areaof the second surface section may be smaller than a lateral area of thefirst surface section. The second surface section may be a centralsection of the first surface section. For example, the second surfacesection and the first surface section may be concentric and/or may havea common central region (e.g., a common center line or a common center).

A lateral cross-sectional area of the larger opening is greater than alateral cross-sectional area of the smaller opening in the samecross-sectional plane. The smaller opening and the larger opening may beformed self-aligned to each other. For example, the positions of boththe larger opening and the smaller opening may be defined by one singlephotolithography process. In other words, it is possible that theposition of the larger opening with respect to the smaller opening isindependent from any alignment process adjusting a follower photomask toan alignment mark defined by a predecessor photomask on the siliconcarbide substrate.

At least part of the implanted first dopants may form at least onecompensation layer portion extending parallel to the trench sidewall,for example parallel to a steep sidewall section of the trench. A dopantdistribution in the compensation layer portion along the verticaldirection may be uniform to a high degree, e.g. over at least 50% oreven at least 70% or even at least 80% of a vertical extension of thecompensation layer portion. For example, a vertical dopant distributionin the compensation layer portion may be approximately uniform(“box-shaped”), e.g. over at least 50% (or 70% or 80%) of the verticalextension of the compensation layer portion.

With the self-aligned formation of the larger opening and the smalleropening with respect to each other, the thickness of and the totalamount of charges in the compensation layer portion may be independentfrom mask alignment tolerances. Mask alignment tolerances may besignificant for some substrates. For example, mask alignment tolerancesmay be significant on substrates like 4H—SiC provided with an off-axiscut. On substrates with off-axis cut, the surfaces on which alignmentmarks are formed are tilted to the main lattice planes. The off-axis cutmay enhance surface distortions and may degrade any alignment markformed thereupon.

With the self-aligned approach, the amount of implanted first dopants inthe compensation layer portion may be precisely defined at highreproducibility. It is possible to provide a superjunction structurewith a narrow tolerance window for a degree of charge balance across thecomplete vertical extension of the superjunction structure or across atleast 50% of the vertical extension of the superjunction structure.Avalanche and breakdown behavior of silicon carbide superjunctiondevices may be precisely predictable.

The compensation layer portions may have a comparatively narrow lateralwidth such that it is possible to provide neighboring first compensationlayers at a comparatively small center-to-center distance. The processmay also facilitate the vertical stacking of compensation layer portionsin a stepwise manner without intermediate epitaxy. As a result, it maybe possible to provide superjunction structures with comparatively largevertical extension at comparatively low effort.

According to an embodiment, the first dopants may be implanted prior toforming the trench. The smaller opening may be formed by forming aspacer along a sidewall of the larger opening. In other words, thesecond process mask for forming the trench may include the first processmask, which has been used for implanting the first dopants, and a spaceralong a sidewall of the larger opening. In this way it is possible toobtain self-aligned first and smaller openings at comparatively loweffort.

According to an embodiment, forming the trench and the compensationlayer portions may include repeating at least once an implant/etchsequence. That is to say, forming the compensation layer portions mayinclude at least two implant/etch sequences: a first implant/etchsequence (e.g., as described above) and repeating said implant/etchsequence in at least one further implant/etch sequence. In general, nimplant/etch sequences may be performed, with n=1, . . . , nmax, nmax≥2.

The implant/etch sequences may include one or more additional processesbetween the implant process and the etch process and/or one or moreadditional processes between two successive implant/etch sequences. Forexample, each implant/etch sequence may include a heat treatment betweenthe implant process and the etch process.

The implant/etch sequence may include implanting first dopants through alarger opening and forming a trench section in a section exposed by asmaller opening. A lateral cross-sectional area of the smaller openingof the n-th implant/etch sequence may be smaller than the lateralcross-sectional area of the larger opening of the n-th implant/etchsequence. The first and the smaller openings used in the sameimplant/etch sequence may be formed self-aligned to each other. Forexample, the smaller opening may be formed by forming a spacer along asidewall of the larger opening.

A lateral cross-sectional area of the larger opening of the (n+1)-thimplant/etch sequence may be as large as or smaller than the lateralcross-sectional area of the smaller opening of the n-th implant/etchsequence. For example, the larger opening of the (n+1)-th implant/etchsequence may correspond to the smaller opening of the n-th implant/etchsequence. For example, the implant/etch sequence may be repeated once ortwice, that is to say, two or three implant/etch sequences may beperformed overall (i.e., nmax=2 or nmax=3, respectively). According toanother embodiment four or more implant/etch sequences may be performed(nmax≥4).

By repeating at least once the implant/etch sequence, at least a firsttrench sidewall may be formed with a staircase shape. The staircaseshape may facilitate the formation of a superjunction structure withcomparatively large vertical extension in a semiconductor material withlow diffusion coefficients for dopants. The stepped trenches mayfacilitate compensation structures with a vertical extension beyond anupper limit for high-energy implants through a flat main surface. Inparticular, providing a trench with a stepped trench sidewall mayincrease the vertical extension of doped regions, which may be formed byan implantation process that uses an energy filter, channeling, variabletilt angle and/or variable implant energy.

A compensation structure with high vertical extension may facilitatesilicon carbide power devices that combine high voltage breakdowncapability with low on-state resistance. In particular, in siliconcarbide devices with a blocking voltage at least 1.2 kV, e.g., at least1.6 kV or at least 3 kV, the on-state resistance of thevoltage-sustaining layer may dominate the on-state losses. Providing thevoltage-sustaining layer with a compensation structure may thereforeeffectively reduce the on-state losses.

In addition, the method may get along without any intermediate epitaxiallayer formation or may facilitate reducing the number of intermediateepitaxial layers. Portions of a compensation structure of a siliconcarbide body can be formed in a self-aligned manner and withoutevaluating alignment marks in different floors. With the self-alignedapproach it may be possible to form comparatively narrow compensationlayer portions. It is also possible to provide neighboring firstcompensation layers at a comparatively small center-to-center distanceand with comparatively high dopant concentration.

The dopant concentration in compensation layer portions formed indifferent floors may be different. Different mean dopant concentrationsof compensation layer portions in different floors may contribute inprecisely shaping the electric field in the blocking mode of the siliconcarbide device. For example, shifting the electric field maximum towardsthe vertical center of the superjunction structure may reduce or avoidTRAPATT (trapped plasma avalanche-triggered transit) oscillations in thesilicon carbide device.

According to an embodiment, further first dopants may be implantedthrough a trench bottom of the trench. The further first dopants mayform a compensation bottom region that extends from the trench bottominto the silicon carbide body. A lateral width of the compensationbottom region and a lateral width of the trench bottom may be equal. Inother embodiments, the lateral width of the compensation bottom regionmay be larger than the lateral width of the trench bottom, e.g. due toat least one of straggling, channeling, diffusion and angle effects. Thecompensation bottom region may further increase the vertical extensionof a superjunction structure. The compensation bottom region may have abox-shaped vertical dopant profile. A mean dopant concentration in thecompensation bottom region may be equal to or may deviate from the meandopant concentration in a neighboring compensation layer portion.

According to another embodiment, the first dopants may be implantedafter forming the trench. For example, after completing the formation ofthe trench, the second process mask with the smaller openings may bereplaced with the first process mask that includes the larger openings,wherein the larger openings may be formed self-aligned to the smalleropenings.

For example, after forming the trench and prior to removing the secondprocess mask, an alignment structure may be formed. The alignmentstructure may be placed in, e.g. may fill, the smaller opening in thesecond process mask. The second process mask may be removed. Anauxiliary spacer may be formed along the sidewall of the exposed uppersection of the alignment structure. A first process mask layer may bedeposited. A planarizing process may remove portions of the firstprocess mask layer deposited above the alignment structure and theauxiliary spacer. The alignment structure and the auxiliary spacer maybe removed selectively with respect to the first process mask layer.

According to another example, the smaller opening of the second processmask may be widened to form the first process mask with the largeropening. For example, wet etching or selectively removing an initialspacer formed prior to the first trench etch may widen the smalleropening.

By implanting the first dopants after completion of the trench, forexample after forming a trench with stepped trench sidewalls and withtwo or more trench sections of different width, it may be possible toform compensation layer portions in different floors and a compensationbottom region by one single implant process in a cost-effective way.

According to an embodiment the larger opening may be formed by wideningthe smaller opening, for example by wet etching. In this way, the largeropenings may be formed at comparatively low-effort.

According to an embodiment, forming the trench may include repeating atleast once an etch sequence, wherein the etch sequence includes forminga trench section in a section of the silicon carbide body exposed by asmaller opening. The smaller opening of the (n+1)-th etch sequence maybe smaller than the smaller opening of the n-th etch sequence. In thisway, it may be possible to form compensation layer portions in differentfloors and a compensation bottom region by one single implant process.

According to an embodiment, the smaller opening of the (n+1)-th etchsequence may be formed by forming a spacer along a sidewall of thesmaller opening of the n-th etch sequence. In this way, it may bepossible to form trenches with stepped sidewalls with precisely definedstep width in a cost-effective way.

According to an embodiment, auxiliary dopants may be implanted into thesilicon carbide body. The auxiliary dopants and the first dopants mayhave complementary conductivity types.

Implanting the auxiliary dopants may include an ion beam implantationwith the ion beam tilted with respect to a vertical direction. Theimplanted auxiliary dopants may form compensation adjustment regions atopposite sides of each trench section. In the compensation adjustmentregions, the mean net dopant concentration may be higher than in themain layer in the same floor.

Each compensation adjustment region may be in contact with twovertically neighboring compensation layer portions. For example, theauxiliary dopants may be implanted into the bottom of the n-th trenchsection before forming the trench section of the (n+1)-th implant/etchsequence. Each compensation adjustment region may be directly below acompensation layer portion along the n-th trench section and laterallynext to a compensation layer portion along the (n+1)-th trench section.

The compensation adjustment regions may smooth discontinuities, whichthe degree of charge balance may show along the vertical direction atthe steps of the stepped trench sidewall. Steep changes of the degree ofcharge balance may result in local peaks of the electric field strengthin a blocking mode of the silicon carbide device. Smoothing chargebalance discontinuities may reduce local maxima of electric fieldstrength and may contribute in improving, e.g., the blocking capabilityof the devices.

According to an embodiment, the silicon carbide body may include a mainlayer. The main layer and the compensation layer portions may havecomplementary conductivity types. The trench may extend into the mainlayer. Compensation regions may, for example, be formed by portions ofthe main layer laterally between neighboring trenches. The compensationregions may further include portions of the main layer laterally betweenneighboring compensation bottom portions.

The compensation bottom region and the compensation layer portionsassigned to the same trench may form one p-type column or layer. Onecompensation region may form one n-type column or layer. Alternatively,the compensation bottom region and the compensation layer portionsassigned to the same trench may form one n-type column or layer and onecompensation region may form one p-type column or layer. A plurality oflaterally arranged n-type and p-type columns or layers may form asuperjunction structure at least in the central active region of thesilicon carbide device.

According to an embodiment, a transistor cell (e.g., a plurality oftransistor cells) may be formed. The transistor cell may include asource region and a body region. The source region and the body regionmay form a pn junction. The source region and the body region may beformed between a first surface of the silicon carbide body and thecompensation layer portions.

The transistor cell may be an insulated gate field effect transistorcell or a junction field effect transistor cell, by way of example. Itis possible to provide power semiconductor switching devices, forexample MOSFETs (metal oxide semiconductor field effect transistors)with a superjunction structure.

According to an alternative embodiment, an anode region may be formedbetween the first surface and the compensation layer portions. It may bepossible to form power semiconductor diodes with the anode region. Theanode region and the compensation layer portions may have the sameconductivity type. The anode region and the compensation regions mayform a main pn junction of the power semiconductor diode. The anoderegion may include a single doped well or may be patterned by dopedregions with a conductivity type opposite to the conductivity type ofthe anode region. The oppositely doped regions may extend from the firstsurface to the compensation regions. The oppositely doped regions and afront side electrode may form Schottky contacts. In this way it may bepossible to provide high-voltage MPS diodes with superjunctionstructure.

According to an embodiment, supplementary dopants may be implanted intothe silicon carbide body after forming the trench. The supplementarydopants and the compensation layer portions may have the sameconductivity type. Implanting the supplementary dopants may include anion beam implantation with the ion beam tilted with respect to thevertical direction. The implanted supplementary dopants may formcompensation connection regions.

For example, the trench sections may be formed to completely or nearlycompletely cut through the auxiliary regions. As a result, compensationlayer portions formed along the sidewalls of neighboring trench sectionsmay be disconnected from each other or may be only weakly connected. Thecompensation connection regions may reliably connect compensation layerportions assigned to neighboring trench sections. In this way it ispossible to provide superjunction structures with each compensationlayer portion electrically connected to a defined electric potential,for example to the anode potential of a power semiconductor diode or tothe emitter potential of a power semiconductor switching device.Continuous doping in the compensation layer portions may contribute inavoiding delayed and/or lossy turn-on behavior of the silicon carbidedevice.

According to another embodiment, a silicon carbide device may include afill structure and compensation layer portions. The fill structure mayextend from a first lateral cross-sectional plane of a silicon carbidebody to a second lateral cross-sectional plane.

The silicon carbide body may have two opposite main surfaces extendingalong lateral directions and a lateral surface area that connects theedges of the two main surfaces. A thickness of the silicon carbide bodyis measured along a vertical direction orthogonal to the lateraldirections.

The fill structure may be stripe-shaped. For example, the fill structuremay laterally extend from one side of a central active region of thesilicon carbide device to the opposite side. According to anotherexample, the fill structure may be needle-shaped with two orthogonallateral extensions within the same order of magnitude. For example, twoorthogonal lateral extensions of a needle-shaped fill structure may beequal or approximately equal. A lateral cross-section of a needle-shapedfill structure may be a regular polygon with or without rounded orbeveled corners, a circle, or an oval by way of example.

The fill structure may have at least one stepped sidewall. The steppedsidewall may include at least two steep sidewall portions laterallyshifted to each other. In a vertical cross-sectional plane orthogonal tothe stepped sidewall, the stepped sidewall may show a staircase patternwith the steep sidewall portions forming the risers (German: Setzstufen)and with flat sidewall portions forming the treads (German: Auftritte).The steep sidewall portions may be vertical or approximately vertical,wherein an angle between each steep sidewall portion and the verticaldirection may be in a range from 0 degree to ±10 degree. The flatsidewall portions may be lateral or approximately lateral, wherein anangle between each flat sidewall portion and the lateral plane may be ina range from 0 degree to ±10 degree. Each flat sidewall portion connectstwo vertically neighboring steep sidewall portions. The stepped sidewallmay include one, two, three or more steps. In other words, each sidewallportion may include one, two, three or more flat sidewall portions.

The compensation layer portions may be doped regions in the siliconcarbide body. Each compensation layer portion may extend along one ofthe steep sidewall portions. For example, compensation layer portionsmay be formed along each steep sidewall portion. Each compensation layerportion may extend from one vertical end of a steep sidewall portion tothe other vertical end of the steep sidewall portion. In other words,the compensation layer portion may extend along the complete steepsidewall portion. A vertical dopant distribution within eachcompensation layer portion may be approximately uniform (“box-shaped”).The mean dopant concentrations in vertically neighboring compensationlayer portions may be equal or may be different.

The staggered arrangement of vertically neighboring compensation layerportions facilitate formation of superjunction structures with avertical extension which is greater than the maximum projected range forthe implanted species in the silicon carbide body for a given maximumimplant energy. In addition, the laterally staggered arrangement ofsteep compensation layer portions may facilitate a highly variablefine-tuning of the charge balance along the vertical direction.

According to an embodiment the fill structure may include two steppedsidewalls on opposite sides of the fill structure. For example, the fillstructure may be symmetric with respect to a vertical plane of symmetry,wherein the plane of symmetry is in in the center of the fill structureand may extend parallel to a lateral longitudinal extension of the fillstructure.

Stepped sidewalls at opposite sides may facilitate the formation oflaterally shifted compensation layer portions in different floors of thesilicon carbide body in an efficient way.

According to an embodiment a compensation bottom region may be formed inthe silicon carbide body. The compensation bottom region may be incontact with a bottom surface of the fill structure. For example, alateral extension of the compensation bottom region and a lateral widthof the bottom surface of the fill structure may be equal orapproximately equal (e.g., within a tolerance of ±10% or ±5%). Avertical distribution of the dopants in the compensation bottom regionmay be approximately uniform. The compensation bottom region may furtherincrease the vertical extension of a superjunction structure, whereinthe charge balance along the complete vertical extension of thesuperjunction structure may be precisely defined at comparatively loweffort.

According to an embodiment, the compensation bottom region and thecompensation layer portions are structurally connected with each other.The fill structure, the compensation bottom region and the compensationlayer portions adjoining the fill structure may form one n-type columnor layer or one p-type column or layer of a superjunction structure. Itis possible, to electrically connect the complete p-type column orn-type column to a defined potential by electrically connecting only onesingle of the compensation layer portions to the defined potential. Incase the silicon carbide device is or includes an MOSFET, the definedpotential may be the source potential of the silicon carbide device.Delayed and/or lossy turn-on behavior of the MOSFET may be avoided bythe proposed superjunction structure.

According to an embodiment, the fill structure includes at least onedielectric structure. The dielectric structure may contribute inavoiding that the fill structure adversely affects the breakdown voltagecapability of the silicon carbide device.

According to an embodiment, compensation regions may be formed in thesilicon carbide body. The compensation regions may be in contact withthe compensation layer portions, wherein each compensation layer portionmay be laterally between the fill structure and one of the compensationregions. The compensation layer portions and the compensation regionsmay form stepped, vertical pn junctions. For example, a compensationregion may form one n-type column or layer or one p-type column orlayer. The compensation layer portions and the compensation bottomregion adjoining a same fill structure may form one oppositely dopedcolumn, e.g., a p-type column for n-type compensation regions or ann-type column for p-type compensation regions. A plurality of suchp-type and n-type columns arranged side-by-side may form a superjunctionstructure. One p-type column and one n-type column that directly adjoinsthe p-type column may form a unit cell of the superjunction structure.Along a lateral line through the unit cell, the line integral across thedoping density of the p type dopants may be in a range from −20% to +20%of the line integral across the doping density of the n type dopants.

The compensation regions may include differently doped sub-regions,wherein each sub-region is in contact with another compensation layerportion. The sub-regions of the compensation regions may result fromdifferently doped sub-layers (floors) of the main layer.

According to an embodiment, an emitter region may be formed in thesilicon carbide body. The emitter region and the compensation layerportions may have the same conductivity type. The emitter region may beformed between a first surface of the silicon carbide body and the firstlateral cross-sectional plane. For example, a p-doped emitter region mayinclude the anode region of a power semiconductor diode or may includethe body regions of transistor cells. The superjunction structure may bepart of a power semiconductor diode with high blocking voltagecapability or part of a power semiconductor switching device, forexample a MOSFET, with high blocking voltage capability. For example,the voltage blocking capability of the silicon carbide device may be atleast 1.2 kV, e.g., at least 1.6 kV or at least 3 kV.

According to an embodiment, a compensation connection region may connecttwo neighboring compensation layer portions. The compensation connectionregion and the compensation layer portions may have the sameconductivity type. The compensation connection region may connect twovertically neighboring compensation layer portions.

According to an embodiment, a compensation adjustment region may be incontact with two neighboring compensation layer portions. Thecompensation adjustment region and the compensation layer portions mayhave complementary conductivity types. Each compensation adjustmentregion may be in contact with two vertically neighboring compensationlayer portions. The compensation adjustment regions may contribute insmoothing discontinuities of the charge balance in the vicinity of thesteps between neighboring steep sidewall portions of the fill structure.

FIGS. 1A-6B concern methods of forming a compensation structure withcompensation regions of a first conductivity type and with compensationlayer portions of a second conductivity type. The first conductivitytype may be the n-type and the second conductivity type may be thep-type. The compensation regions and the compensation layer portions mayform a regular pattern of lateral pn junctions.

The methods include a combination of masked ion implantation and maskedtrench etching. Openings in the mask for ion implantation and openingsin the mask for trench etching may be formed self-aligned to each other.In FIGS. 1A-1B, 3A-3N and 4A-4D etching trenches follows implantingions. In FIGS. 2A-2B and 6A-6C implanting ions follows etching trenches.

FIG. 1A shows a silicon carbide body 100 and a first process mask 410formed on a first surface 101 of the silicon carbide body 100. Thesilicon carbide body 100 may be a portion of a silicon carbidesubstrate. The silicon carbide substrate may include a plurality ofsilicon carbide bodies arranged side-by-side and laterally connected toeach other. From each silicon carbide body 100 the semiconductor die(chip) of one power semiconductor device may be formed. The firstsurface 101 of the silicon carbide body 100 may be a section of a mainsurface at a front side of the silicon carbide substrate.

The silicon carbide body 100 may include a doped main layer 130. Themain layer 130 may be formed by epitaxy. The main layer 130 may have afirst conductivity type. For example, the main layer 130 may be n-doped.The first process mask 410 may include one single homogeneous layer ormay include two or more sub-layers from different materials. Largeropenings 411 in the first process mask 410 expose first surface sectionsof the first surface 101.

First dopants are implanted through the larger openings 411 into thesilicon carbide body 100. For example, an ion beam may be directed ontothe first surface 101. The first dopants form doped auxiliary regions170 in sections of the silicon carbide body 100 below the largeropenings 411. The auxiliary regions 170 have a second conductivity type.The auxiliary regions 170 and the main layer 130 may form pn junctions.The ion beam may be controlled and/or modified to generate anapproximately uniform vertical distribution of the first dopants in theauxiliary regions 170.

A second process mask 420 is formed. The second process mask 420 may beformed by modifying the first process mask 410. For example, the largeropenings 411 may be transformed into smaller openings 421. A lateralcross-section of the smaller openings 421 is smaller than a lateralcross-section of the larger openings 411. For circular openings, thediameter of the smaller openings 421 is smaller than the diameter of thelarger openings 411. For rectangular openings with or without rounded orbeveled corners, at least one lateral width of the smaller openings 421is smaller than a corresponding lateral width of the larger openings411. The first and smaller openings 411, 421 may be concentric orapproximately concentric.

For example, each smaller opening 421 may be formed by forming a spacer431 along the inner sidewall of a larger opening 411. Forming the spacer431 may include depositing a conformal auxiliary layer on the firstprocess mask 410. The auxiliary layer is sufficiently thin to notcompletely fill the larger openings 411. A directed etching process mayremove lateral portions of the auxiliary layer on the first process mask410 and on the first surface 101. Residuals of the auxiliary layer formthe spacers 431 along the inner sidewalls of the larger openings 411 ofFIG. 1A.

FIG. 1B shows the second process mask 420 with the smaller openings 421.The smaller openings 421 expose second surface sections of the firstsurface 101 and are preferentially self-aligned to the larger openings411 of FIG. 1A. The second surface sections are central sub-sections ofthe first surface sections.

Trenches 800 are formed in the silicon carbide body 100 directly belowthe smaller openings 421. Forming the trenches 800 may includeanisotropic etching, for example reactive ion beam etching. A verticalextension of the trenches 800 may be equal to or smaller than a verticalextension of the auxiliary regions 170. Forming the trenches 800includes removing a central portion of each auxiliary region 170.Residual portions of each auxiliary region 170 form compensation layerportions 181. Each compensation layer portion 181 extends along a steepsidewall section 811 of the trench 800.

FIG. 2A shows trenches 800 formed in a main layer 130 of a siliconcarbide body 100 directly below smaller openings 421 of a second processmask 420. A first process mask 410 with larger openings 411, which arewider than the smaller openings 421, may be formed. For example, anisotropic etch, e.g., a wet etch, may laterally recess the secondprocess mask 420, wherein the smaller openings 421 transform into thelarger openings 411. First dopants are implanted through the largeropenings 411 into the silicon carbide body 100.

According to FIG. 2B, the implanted first dopants form compensationlayer portions 181 directly below the first surface 101 and extendingalong steep sidewall sections 811 of the trench 800. In addition, thefirst dopants form compensation bottom portions 189 below the trenches800. Each compensation bottom portion 189 extends from a trench bottom809 into the main layer 130.

FIGS. 3A-3N illustrate a method using trenches 800 with stepped trenchsidewalls 801 for forming a compensation structure 800, wherein trenchsections in different floors of a silicon carbide body may havedifferent mean widths.

The silicon carbide body 100 includes a main layer 130 of a firstconductivity type. A process mask layer is deposited on the firstsurface 101 of the silicon carbide body 100. A photoresist layer isdeposited on a top surface of the process mask layer. A photolithographyprocess forms a photoresist mask 490 from the photoresist layer. Thepattern of the photoresist mask 490 is transferred into the process masklayer, wherein a first process mask 410 with larger openings 411 isformed.

FIG. 3A shows the larger openings 411 exposing first surface sections ofthe first surface 101 of the silicon carbide body 100. The first processmask 410 is sufficiently thick to locally block deep verticalimplantations of dopants into the silicon carbide body 100. For example,the first process mask 410 may include silicon oxide or a metal, e.g.tungsten (W). The first process mask 410 may have a sufficient thicknessto mask implants of aluminum ions, nitrogen ions and/or boron ions withimplant energy up to 25 MeV. For example, the thickness of the processmask 410 may be in a range from 0.3 μm to 37 μm, from 0.5 μm to 12 μm orfrom 1 μm to 4 μm.

The photoresist mask 490 may be removed. Dopants are implanted throughthe larger openings 411 into a first floor F1 of the silicon carbidebody 100. The implantation beam may be modified and/or controlled in waysuch that the vertical range of the implanted dopants shows anapproximately uniform distribution within the first floor F1.

According to FIG. 3B the implanted first dopants form first auxiliaryregions 171 in the vertical projection of the larger openings 411 in thefirst floor F1. A vertical extension of the first floor F1 may be in arange from 0.2 μm to 20 μm, e.g. from 0.5 μm to 7 μm or from 1 μm to 3μm, by way of example. Within the first auxiliary regions 171 thevertical dopant distribution may be approximately uniform.

A first auxiliary layer 460 may be formed at the front side of thesilicon carbide body 100. The first auxiliary layer 460 may coverlateral and vertical surfaces at approximately uniform thickness.

FIG. 3C shows the first auxiliary layer 460 covering a top surface ofthe first process mask 410, lining sidewalls of the larger openings 411of FIG. 3B and covering the first surface sections. A thickness of thefirst auxiliary layer 460 is smaller than 50% or even smaller than 25%of the smallest width of the larger openings 411. The first auxiliarylayer 460 may be or may include a silicon oxide layer, by way ofexample.

Lateral portions of the first auxiliary layer 460 are removed. Forexample, anisotropic etching like reactive ion beam etching mayselectively remove the lateral portions of the first auxiliary layer460.

As illustrated in FIG. 3D, residuals of the first auxiliary layer 460 ofFIG. 3C form first spacers 431 along inner sidewalls of the largeropenings 411. The first spacers 431 and the first process mask 410 ofFIG. 3B form a second process mask 420. The second process mask 420includes smaller openings 421 that expose central sections of the firstauxiliary regions 171. The second process mask 420 with the smalleropenings 421 is used as etch mask for forming trenches. For example, thesecond process mask 420 masks reactive ion beam etching.

FIG. 3E shows first trench sections 810 extending from the first surface101 into the first auxiliary regions 171. Residuals of the firstauxiliary regions 171 of FIG. 3D at both lateral sides of the firsttrench sections 810 form compensation layer portions 181. A verticalextension of the compensation layer portions 181 may be equal to ordeeper than a vertical extension of the first trench sections 810. Inparticular, the vertical extension of the compensation layer portions181 is equal to the vertical extension of the first trench sections 810.

The vertical extension of the first trench sections 810 may be equal toor shallower than a vertical extension of the first auxiliary region171. In the illustrated embodiment, the vertical extension of the firsttrench sections 810 is smaller than the vertical extension of the firstfloor F1. Residuals of the first auxiliary regions below the firsttrench sections 810 and below the compensation layer portions 181 formbottom layers 179.

The second process mask 420 may mask a further implant of first dopants,e.g. p-type dopants like aluminum atoms, into a second floor F2 of thesilicon carbide body 100. In other words, the second process mask 420for the first floor F1 may be used as first process mask 410-F2 withlarger openings 412 for masking ion implantation of further firstdopants into the second floor F2.

FIG. 3F shows second auxiliary regions 172 extending from a lower edgeof the bottom layer 179 into the silicon carbide body 100. A lateralextension of the second auxiliary regions 172 may be equal to or smallerthan a lateral extension of the first trench sections 810. In someembodiments, lateral straggling may result in second auxiliary regions172 with a lateral extension that is larger than a lateral extension ofthe first trench sections 810.

A vertical distribution of the first dopants in the second floor F2 maybe approximately uniform. A mean dopant concentration in the secondauxiliary regions 172 may be equal to a mean dopant concentration in thefirst compensation layer portions 181 in the first floor F1 or maydeviate from a mean dopant concentration in the compensation layerportions 181. The second floor F2 may have the same vertical extensionor approximately the same vertical extension as the first floor F1.Alternatively, the vertical extension of the second floor F2 may deviatesignificantly from the vertical extension of the first floor F1, whereinthe vertical extension of the second floor F2 may be greater or may besmaller than the vertical extension of the first floor F1. A secondauxiliary layer 470 may be deposited on the front side of the siliconcarbide body 100.

FIG. 3G shows the second auxiliary layer 470 covering at uniformthickness a top surface of the first process mask 410-F2 with largeropenings 412 for masking ion implantation into the second floor F2, thesidewalls of the larger openings 412, the sidewalls of the first trenchsections 810, and the bottom of the first trench section 810. Ananisotropic etch may selectively remove the lateral portions of thesecond auxiliary layer 470. Residuals of the second auxiliary layer 470form further spacers 432.

As illustrated in FIG. 3H, the first process mask 410-F2 of FIG. 3G andthe spacers 431, 432 form a second process mask 420-F2 with smalleropenings 422 for masking a trench etching into the second floor F2. Thefurther spacers 432 line the sidewalls of the smaller openings 421 inthe first process mask 410-F2 of FIG. 3F and the sidewalls of the firsttrench sections 810. The second process mask 420-F2 masks a furtheranisotropic etching that forms second trench sections 820.

FIG. 3I shows the second trench sections 820 extending from the bottomof the first trench sections 810 into the second floor F2. The secondtrench sections 820 may reach down to the bottom of the second floor F2or may not reach the bottom of the second floor F2. Residuals of thesecond auxiliary regions 172 of FIG. 3H at opposite sides of each secondtrench section 820 form further compensation layer portions 181. Belowthe compensation layer portions 181 residuals of the bottom layers 179shown in FIG. 3H form compensation connection regions 186 verticallybelow the compensation layer portions 181 in the first floor F1. Eachconnection region 186 is in direct contact with a vertically neighboringcompensation layer portion 181 and with a laterally neighboringcompensation layer portion 181.

Residuals of the second auxiliary regions 172 below the second trenchsections 820 and below the compensation layer portions 181 in the secondfloor F2 form further bottom layers 179. Further first dopants may beimplanted through the smaller openings 422 of the second process mask420-F2.

As illustrated in FIG. 3J, the further first dopants form compensationbottom regions 189 in the third floor F3. The first and the secondtrench sections 810, 820 form a trench 800 with stepped trench sidewalls801. The compensation bottom regions 189 extend from the trench bottom809 of the trenches 800 into the third floor F3. Below the compensationlayer portions 181 in the second floor F2, residuals of the bottomlayers 179 of FIG. 3I form further compensation connection regions 186.The further compensation connection regions 186 connect the compensationbottom portion 189 with two compensation layer portions 181 formed atopposite sidewalls of the second trench section 820. The second processmask 420-F2 may be removed.

According to FIG. 3K, compensation layer portions 181 formed alongopposite sidewalls of the same trench 800 and a compensation bottomportion 189 formed below the trench 800 are interconnected with eachother and form first columns, e.g. p-type columns, of a compensationstructure 180. Sections of the main layer 130 between neighboring firstcolumns form compensation regions 182. The compensation regions 182 formsecond columns, e.g. n-type columns, of a compensation structure 180.The n-type columns and the p-type columns form a regular pattern ofvertical pn junctions with steps.

The trenches 800 may be filled with a suitable material. Maskedimplantations may form further doped regions in the first floor F1.

FIG. 3L shows fill structures 190 filling the trenches 800 of FIG. 3K.The fill structures 190 may include one or more dielectric materials.For example, the fills structures 190 may include exclusively siliconoxide or silicon oxide in combination with at least one furthermaterial. The further materials may include silicon nitride, dopedsemiconductor material, and/or intrinsic semiconductor material.

A mean dopant concentration in each of the first floor F1, the secondfloor F2 and the third floor F3 may be selected in a way that in each ofthe floors F1, F2, F3 substantially charge compensation with thecompensation layer portions 181 is given. Since absolute compensationmay not be accomplished due to process scattering or other reasons, oneor more of the floors may be deliberately differ from exact chargecompensation. As an example, doping in first floor F1 may be selected inorder to not fully compensate charge of layer portion 181 in first floorF1; doping in second floor F2 may be selected to substantiallycompensate charge of layer portion 181 in second floor F2 and doping inthird floor F3 may be selected to over-compensate charge of layerportion 181 in third floor F3. Of course, the inverse scheme of dopingor another scheme of doping may be chosen.

For the case of filling the trenches with doped semiconductor material,this doping level can be taken into account when choosing the dopingparameter of the compensation layers and/or choosing the doping levelsof first, second and third floors F1, F2, F3, respectively, to obtainthe desired degree of charge balance. Deep shielding portions 169 of theconductivity type of the compensation layer portions 181 may be formedalong the first surface 101. Each deep shielding portion 169 may form adirect vertical contact with one single compensation layer portion 181or may overlap with one single compensation layer portion 181.

A top layer F0 may be formed by epitaxy on the first floor F1, may beformed by an upper portion of the first floor F1 or may be providedbetween the first surface 101 and the first floor prior to forming thetrenches 800. Masked ion implantations into the top layer F0 may formdoped regions of transistor cells. Gate trenches 850 may be formed inthe top layer F0.

FIG. 3M shows the gate trenches 850. The gate trenches 850 extendthrough the top layer F0 and expose the fill structures 190 and topsurfaces of the compensation layer portions 181 in the first floor F1.The gate trenches 850 may be stripe-shaped. A lateral longitudinal axisof the gate trenches 850 may extend parallel to a lateral longitudinalaxis of the fill structures 190. According to another embodiment, thelateral longitudinal axis of the gate trenches 850 may extend tilted,e.g. orthogonal, to a lateral longitudinal axis of the fill structures190. The doped regions in the top layer F0 may include top shieldingportions 168, source regions 110, body regions 120, and current spreadregions 137.

A gate dielectric 159 may be formed that lines at least one of thesidewalls of each gate trench 850. Forming the gate dielectric 159 mayinclude thermal oxidation of exposed silicon carbide and/or depositionof one or more dielectric materials. One or more conductive materialsmay be deposited into the gate trenches 850.

FIG. 3N shows transistor cells TC formed in the top layer F0. Eachtransistor cell TC includes a gate structure 150 formed in one of thegate trenches 850 of FIG. 3M. The gate structures 150 include aconductive gate electrode 155 and a gate dielectric 159. The gatedielectric 159 is formed between the gate electrode 155 and the siliconcarbide body 100 at least along an active first gate sidewall 151 of thegate structure 150.

Each transistor cell TC includes a body region 120 of the secondconductivity type. The body region 120 is in direct contact with theactive first gate sidewall 151. A source region 110 is formed betweenthe first surface 101 and the body region 120. A current spread region137 may be formed between the body region 120 and a neighboringcompensation region 182. The current spread region 137 and theneighboring compensation region 182 may form a unipolar junction or mayhave the same mean net dopant concentration. The source region 110 andthe current spread region 137 have the first conductivity type. The bodyregion 120 forms a first pn junction with the current spread region 137and a second pn junction with the source region 110.

A shielding region 160 may include a top shielding portion 168 and thedeep shielding portion 169 of FIG. 3L. The shielding region 160 extendsalong an inactive second gate sidewall 152 of the gate structure 150.Each shielding region 160 is in direct contact with a compensation layerportion 181.

FIGS. 4A-4D illustrate a method for at least partially compensatingexcess dopants. For example, the compensation connection regions 186 ofFIG. 3N may provide a local excess of dopants. A local excess of dopantstypically results in a significant drop of the degree of charge balance.

In FIG. 4A a vertical extension of the first trench section 810 issmaller than the vertical extension of the first floor F1. Bottom layers179 are formed as described with reference to FIG. 3E. Auxiliary dopantsof the first conductivity type may be implanted into a section of thesilicon carbide body 100 directly below and/or into the bottom layers179. Implanting the auxiliary dopants may include a tilted implantation,wherein implant angles 4 between a vertical direction 104 and the ionbeam 105 may be in a range from 5° to 20° and from −5° to −20°.

The implanted auxiliary dopants form intermediate layers 885 below thefirst trench sections 810. The intermediate layers 885 may be n dopedlayers formed below p doped bottom layers 179. The intermediate layers885 and the bottom layers 179 may partly overlap, wherein in theoverlapping portion the intermediate layer 885 may partly compensate thedoping in the bottom layer 179. A lateral width of the intermediatelayer 885 may be greater than a lateral width of the first trenchsection 810 such that the intermediate layer 885 includes sectionsdirectly below the compensation layer portions 181 in the first floorF1.

Further first dopants are implanted at comparatively high mean energythrough the bottom of the first trench sections 810 to form secondauxiliary regions 172 as described with reference to FIG. 3E and FIG.3F.

FIG. 4B shows the second auxiliary regions 172 as described withreference to FIG. 3F. Residuals of the intermediate layer 885 of FIG. 4Aform compensation adjustment regions 185 at both sides of each secondauxiliary region 172.

A second trench section 820 may be formed as described with reference toFIG. 3H and FIG. 3I, wherein a further bottom layer 179 and a furtherintermediate layer 885 may be formed as described with reference to FIG.4A.

As illustrated in FIG. 4C, the compensation adjustment regions 185 inthe second floor F2 may be formed directly below the compensationconnection regions 186 in the first floor F1 and in lateral contact withthe compensation connection regions 186 in the second floor F2.Compensation bottom regions 189 may be formed as described withreference to FIG. 3J.

According to FIG. 4D, residuals of the intermediate layer 885 in thethird floor F3 may form compensation adjustment regions 185 on oppositesides of each compensation bottom region 189. The compensationadjustment regions 185 in the third floor F3 may be formed directlybelow the compensation connection regions 186 in the second floor F2 andin lateral contact with the compensation bottom region 189.

In the method illustrated in FIGS. 5A to 5C and in the method accordingto FIG. 5D one single implant forms all compensation layer portions 181and the bottom compensation region 189.

FIG. 5A shows a second process mask 420 with a smaller opening 421. Afirst trench section 810 is formed in the vertical projection of thesmaller opening 421. The first trench section 810 may extend from thefirst surface 101 into a first floor F1 of the silicon carbide body 100.According to an embodiment, the second process mask 420 may include afirst process mask 410 and a spacer 431 lining a larger opening in thefirst process mask 410.

A further spacer 432 is formed that lines the inner sidewall of thesmaller opening 421 and the inner sidewall of the first trench section810. The second process mask 420 and the further spacer 432 form afurther second process mask 420-F2 with smaller openings 422, which maymask a further etching into the silicon carbide body 100. A secondtrench section 820 is formed in an exposed section of the trench bottomof the first trench section 810.

As illustrated in FIG. 5B, the second trench section 820 may extend fromthe trench bottom of the first trench section 810 into a second floor F2of the silicon carbide body 100. The first trench section 810 and thesecond trench section 820 form a trench 800.

A first process mask 410 with larger openings 411 is formed, wherein thelarger openings 411 expose the trenches 800 and collar surface sections101 c of the first surface 101 around the openings of the trenches 800.For example, the spacers 432, 431 may be selectively removed to lay openand recover the first process mask 410.

First dopants are implanted through the larger openings 411, wherein theimplant beam is controlled and/or modified to obtain an approximatelyuniform distribution of the implanted first dopants along the verticaldirection, e.g. over at least 50% or even at least 70% or even at least80% of the vertical extension of each implant region.

According to FIG. 5C the implanted first dopants form compensation layerportions 181 and compensation bottom regions 189 in one singleimplantation process using one single implantation mask.

The compensation layer portions 181 may be formed along all steepsidewall sections 811 of the trenches 800. The maximum implant depth andthe vertical extension of the trench sections 810, 820 may be equal. Inan alternative, the maximum implant depth may be smaller than thevertical extension of the trench sections 810, 820. In both cases, afurther, tilted implant may form compensation connection regions asdescribed with reference to FIGS. 6A-6B. In the illustrated alternative,the maximum implant depth is greater than the vertical extension of thetrench sections 810, 820. The implant forms compensation connectionregions 186 directly below each compensation layer portion 181.

The compensation bottom regions 189 extend from the bottom surface 809of the trenches 800 into the third floor F3. Compensation adjustmentregions may be formed as described with reference to FIGS. 6A to 6B. Atop layer may be formed on the first floor F1, e.g. by epitaxy, and gateelectrodes may be formed in the top layer as described with respect toFIG. 3N, by way of example.

FIG. 5D refers to a method with a silicon carbide body 100 including atop layer F0 between the first floor F1 and the first surface 101 priorto forming the trenches 800. A process mask 410 as described in FIGS.5A-5C may be formed on the top layer F0 and is used to form gatetrenches 850 in the top layer F0. After forming the gate trenches 850,the first and second trench sections 810, 820 are formed at the bottomof the gate trenches 850 in the first and second floors F1, F2.

FIG. 5D shows that the final implant mask (first process mask 410),which is used for forming the compensation layer portions 181 and thecompensation bottom regions 189, may be identical with the gate trenchetch mask or may be obtained from the gate trench etch mask by modifyingthe gate trench etch mask. Modifying the gate trench etch mask mayinclude spacer formation or wet etching, by way of example. Forming thegate trenches 850 in the top layer F0 may also be combined with themultiple implant/etch sequence described with reference to FIGS. 3A-3N.

FIGS. 6A and 6B refer to a method that connects vertically neighboringcompensation layer portions 181 at a process stage after forming atrench 800 with at least two trench sections 810, 820.

According to FIG. 6A the vertical extension of the first trench sections810 and the vertical extension of the first floor F1 are equal. Thevertical extension of the second trench sections 820 and the verticalextension of the second floor F2 are equal. Vertically neighboringcompensation layer portions 181 may be disconnected from each other.

At least two symmetric, tilted implantations may implant supplementarydopants of the conductivity type of the compensation layer portions 181into the trench sidewalls 801. Implant angles φ between a verticaldirection and the ion beam may be in a range from 5° to 20° and from −5°to −20°.

As illustrated in FIG. 6B the implanted supplementary dopants formcompensation connection regions along the edges of the stepped trenchsidewalls 801 and along the edges between the trench sidewalls 801 andthe trench bottom 809. The compensation connection regions 186 connectthe compensation bottom portions 189 and the compensation layer portions181 formed along the same trench 800.

FIG. 7 shows a silicon carbide device 500 including transistor cells TCand a compensation structure 180. The silicon carbide device 500includes a silicon carbide body 100 that may be processed as describedabove in connection with FIGS. 1A-1B, FIGS. 2A-2B, FIGS. 3A-3N, FIGS.4A-4B, FIGS. 5A-5C and FIGS. 6A-6B.

A first surface 101 at a front side and a second surface 102 at a rearside of the silicon carbide body 100 run approximately parallel to eachother. A thickness of the silicon carbide body 100 is given along avertical direction 104. The vertical direction 104 may be parallel to asurface normal on a planar first surface 101 or to a surface normal of amean plane of a ripped first surface 101. The first surface 101 may betilted to a main crystal plane of the silicon carbide lattice. Forexample, the first surface 101 may be tilted to the (0001) plane of asilicon carbide body 100 with hexagonal crystal lattice by an off-axisangle of about 4 degree.

The transistor cells TC may be formed along trench gate structures 150that extend from the first surface 101 into the silicon carbide body100. The gate structures 150 may be stripe-shaped. That is to say: alength of the gate structures 150 along a lateral first direction isgreater than a width of the gate structures 150 along a lateral seconddirection orthogonal to the first direction. The gate structures 150 maybe long stripes extending along a lateral longitudinal direction througha central active region of the silicon carbide body 100. In otherembodiments, lateral cross-sections of the gate structures 150 may becircles, ovals or regular polygons, e.g. squares or hexagons, with orwithout rounded or beveled corners.

The gate structures 150 include a conductive gate electrode 155 that mayinclude or consist of a heavily doped polycrystalline silicon layerand/or a metal-containing layer. A gate dielectric 159 separates thegate electrode 155 from the silicon carbide body 100 along at least oneside of the gate structure 150. The gate dielectric 159 may include orconsist of thermally grown or deposited silicon oxide, silicon nitride,silicon oxynitride, another deposited dielectric material or anycombination thereof. A thickness of the gate dielectric 159 may beselected to obtain transistor cells TC with a threshold voltage in arange from 1.0 V to 8 V. The gate structures 150 may exclusively includethe gate electrode 155 and the gate dielectric 159 or may includefurther conductive and/or dielectric structures in addition to the gateelectrode 155 and the gate dielectric 159.

The gate structures 150 may be equally spaced and/or may have equalwidth. A center-to-center distance between neighboring gate structures150 may be in a range from 1 μm to 10 μm, e.g., from 2 μm to 5 μm. Alength of the gate structures 150 may be up to several millimeters. Avertical extension of the gate structures 150 may be in a range from 0.3μm to 5 μm, e.g., in a range from 0.5 μm to 2 μm. At the bottom, thegate structures 150 may be rounded.

Opposing first and second gate sidewalls 151, 152 of each of the gatestructures 150 may run essentially along the vertical direction 104 ormay be tilted with respect to the vertical direction 104 by a taperangle. In the latter case, the gate structures 150 may taper withincreasing distance to the first surface 101. The taper angle betweenthe gate sidewalls 151, 152 and the vertical direction 104 at the firstsurface 101 may be chosen according to the alignment of the crystal axesand/or according to the off-axis angle.

For example, the absolute value of the taper angle between the firstgate sidewall 151 and the vertical direction 104 may deviate from theabsolute value of the off-axis angle by not more than ±1° (e.g., in thecase of 4H—SiC the taper angle may range from at least 3° to at most5°). The taper angle may, however, deviate from the off-axis angle inorientation. The taper angle between the second gate sidewall 152, whichis opposite to the first gate sidewall 151, and the vertical directionmay be oriented opposite to the taper angle of the first sidewall 151.The larger the taper angle, the narrower the gate structure 150 becomesstarting from the first surface 101.

In general, at least the first gate sidewall 151 may run essentiallyalong a crystal plane of the silicon carbide body 100 in which chargecarrier mobility is high (e.g., one of the {11-20} or the {1-100}crystal planes). The first gate sidewall 151 may be an active sidewall,that is to say, the channel region may run along the first gate sidewall151. In some embodiments, the second gate sidewall 152 may also be anactive sidewall (e.g., in the case of a vertical trench gate structure150). In other embodiments, (e.g. in case of a tapering trench gatestructure 150) the second gate sidewall 152 may be an inactive sidewall.

Doped regions in portions of the silicon carbide body 100 laterallybetween two neighboring gate structures 150 may include a source region110, a body region 120, a current spread region 137 and a shieldingregion 160. The source region 110 and the current spread region 137 havea first conductivity type. The body region 120 and the shielding region160 have the complementary second conductivity type. In the illustratedembodiment, the first conductivity type is n-type and the secondconductivity type is p-type. In alternative embodiments, the firstconductivity type may be p-type and the second conductivity type may ben-type.

The source region 110, the body region 120 and the current spread region137 may be in direct contact with the first gate sidewall 151 of a firstgate trench structure 150. The body region 120 separates the sourceregion 110 and the current spread region 137. The source region 110 maybe formed between the first surface 101 and the body region 120. Thebody region 120 and the source region 110 form a pn junction. The bodyregion 120 and the current spread region 137 form a pn junction.

A vertical extension of the body region 120 corresponds to a channellength of the transistor cells TC and may be in a range from 0.2 μm to1.5 μm. Along the lateral direction orthogonal to the cross-sectionalplane, the source region 110 may extend without interruptions along thecomplete lateral length of the gate structure 150.

The shielding region 160 is formed between the body region 120 and theinactive second gate sidewall 152 of a neighboring second gate structure150. The body region 120 and the shielding region 160 may form aunipolar junction. The shielding region 160 extends along the inactivesecond gate sidewall 152 of the second gate structure 150 from the firstsurface 101 into the silicon carbide body 100. A vertical extension ofthe shielding regions 160 is greater than a vertical extension of thegate structures 150.

A maximum dopant concentration in the shielding region 160 may be higherthan a maximum dopant concentration in the body region 120. A verticaldopant concentration profile in the shielding region 160 may have alocal maximum at a position below the trench gate structure 150. Alongthe inactive second gate sidewall 152 a dopant concentration in theshielding region 160 may be higher, i.e., at least ten times as high asa dopant concentration in the body region 120 along the active firstgate sidewall 151. Along the lateral direction orthogonal to thecross-sectional plane, the shielding region 160 may extend withoutinterruptions along the complete lateral length of the gate structure150.

The compensation structure 180 may be formed in a main layer 130. Themain layer 130 is formed between the gate structures 150 and the secondsurface 102. The main layer 130 may be a layer grown by epitaxy. Themain layer 130 may be uniformly doped or may have a non-uniform verticaldistribution of dopants. For example, the main layer 130 may include twoor more vertically stacked floors F1, . . . , Fn with n greater 1. Eachfloor F1, F2, . . . may have a uniform dopant distribution or may have anon-uniform vertical dopant profile. The floors F1, F2, . . . may havethe same vertical extension or at least one of the floors F1, F2, . . .may have a vertical extension different from at least one of the otherfloors F1, F2, . . . . A vertical extension of each floor F1, F2, . . .may be in a range from 0.5 μm to 7 μm, for example from 1 μm to 5 μm.The floors F1, F2 . . . may have the same mean dopant concentration orat least one of the floors F1, F2, . . . may have a mean dopantconcentration different from at least one of the other floors F1, F2, .. . . For example, the mean dopant concentration in each floor F(n+1)may be lower than the mean dopant concentration in floor Fn.

A heavily doped contact portion or drain layer 139 may be formed betweenthe main layer 130 and the second surface 102. The contact portion 139may have the first conductivity type for a power MOSFET or a diode. ForIGBTs the backside contact or backside emitter region may be p-doped.The contact portion 139 may be or may include a substrate portionobtained from a crystalline ingot and/or may include a heavily dopedportion of a layer formed by epitaxy. Along the second surface 102, adopant concentration in the contact portion 139 is sufficiently high toensure a low-resistive ohmic contact between the contact portion 139 anda metal structure.

The main layer 130 may directly adjoin the contact portion 139.Alternatively, a spacer layer may separate the main layer 130 and thecontact portion 139. The spacer layer may have the first conductivitytype and may include a buffer layer. A vertical extension of the spacerlayer may be between 0.5 μm and 50 μm or between 1 μm and 10 μm. A meandopant concentration in the spacer layer may be in a range from 3*10¹⁷cm⁻³ to 10¹⁹ cm⁻³, by way of example.

The compensation structure 180 in the main layer 130 may include asuperjunction structure with first columns of the first conductivitytype and with second columns of the second conductivity type. The firstand second columns of the compensation structure 180 arecharged-balanced to a predefined degree. For example, the lateral lineintegral through a first column deviates by not more than ±20%, by notmore than ±10% or even by not more than ±5% from the lateral lineintegral through a second column in the same lateral plane. The lateralline integrals are taken along a lateral direction perpendicular to a pnjunction between the first column and the second column.

Each second column may include compensation layer portions 181 and abottom compensation region 189, wherein the compensation layer portions181 and the bottom compensation region 189 may be connected to eachother and may be in contact with a same fill structure 190.

The fill structure 190 extends from a top surface of the first floor F1of the main layer 130 into the main layer 130. The fill structure 190has stepped sidewalls 191. Each stepped sidewall 191 may include two ormore steep sidewall portions 192, which are laterally shifted to eachother. The steep sidewall portions 192 may be vertical or may deviatefrom the vertical direction by up to ±10 degree, by way of example. Flatsidewall portions 193 connect neighboring steep sidewall portions 192.The flat sidewall portions 193 may be lateral or approximately lateral,wherein an angle between each flat sidewall portion 193 and the lateralplane may be in a range from 0 degree to ±25 degree, e.g. from 0 degreeto ±10 degree.

The compensation layer portions 181 may extend at uniform thicknessalong each steep sidewall portion 192 on opposite sides of the fillstructure 190. Pairs of compensation layer portions 181 may be formed onopposite sides of the fill structure 190 in the same floor F1, F2, . . .. Compensation layer portions 181 formed in different floors F1, F2, . .. may be laterally shifted to each other. The compensation bottom region189 extends from a bottom surface 199 of the fill structure 190 into themain layer 130. Each second column may be structurally connected with atleast one shielding region 160. For example, a compensation layerportion 181 of a second column may be in direct contact with a shieldingregion 160.

A lateral width of a compensation layer portion 181 may be in a rangefrom 50 nm to 2 μm. A mean net dopant concentration in a compensationlayer portion 181 may be in a range from 10¹⁷ cm⁻³ to 10¹⁹ cm⁻³. Thelaterally integrated net dopant concentration in each compensation layerportion 181 may be in a range of 10¹² cm⁻² to 10¹¹ cm⁻² or in a rangefrom 5·10¹² cm⁻² to 2·10¹³ cm⁻² to enable full depletion in the blockingstate of the device. For example, the laterally integrated net dopantconcentration in each second column and in each first column may be in arange within ±20% of the half breakdown charge of crystalline siliconcarbide, e.g., in a range within from 0.8*10¹³ cm⁻² to 1.2*10¹³ cm⁻².For example, a compensation layer portion 181 may have a lateral widthof 50 nm and a mean net dopant concentration of 10¹⁹ cm⁻³ or a lateralwidth of 2 μm and a mean net dopant concentration of 10¹⁷ cm⁻³.

The fill structure 190 may be a homogeneous structure or may be alayered structure including two or more different materials. The fillstructure 190 may include dielectric material, conductive materialand/or intrinsic semiconductor material.

For example, the fill structures 190 may be completely formed fromsilicon oxide or may include at least one dielectric material differentfrom silicon oxide, wherein a total temperature coefficient of the fillstructure 190 may be closer to the temperature coefficient ofsingle-crystalline silicon carbide than the temperature coefficient ofsilicon oxide. For example, the fill structures 190 may include at leastone of silicon nitride and a silicon oxide. The silicon oxide mayinclude silicon oxide formed by using TEOS (tetraethylorthosilane) asprecursor material, a HDP (high density plasma) silicon oxide, and/or anoxide densified after deposition.

Each first column of the superjunction structure 180 may include acompensation region 182. Each compensation region 182 includes a sectionof the main layer 130 laterally between neighboring second columns. Thecompensation regions 182 may be substantially uniformly doped along thevertical direction. Each compensation region 182 may includecompensation subsections 1821, 1822, . . . . Each compensationsubsection 1821, 1822, . . . may be formed in another floor F1, F2, . .. . The vertical extensions of the compensation subsections 1821, 1822,. . . may be equal or may be different.

The mean dopant concentrations in the compensation subsections 1821,1822, . . . may be equal or may be different. For example, the meandopant concentration of a compensation subsection 1821, 1822, . . . maydepend on the width of the compensation subsection 1821, 1822, . . . .For example, in a narrower compensation subsection 1821, 1822, . . . themean dopant concentration may be higher as in a wider compensationsubsection 1822, 1823, . . . . A higher mean dopant concentration may atleast partly compensate a smaller lateral extension with respect to thetotal amount of dopants in the compensation subsection 1821, 1822, . . .. For example, for each compensation subsection 1821, 1822, . . . theintegrated dopant concentration along a lateral cross-sectional linethrough the respective compensation subsection 1821, 1822, . . . may bein a range of ±10% of the same target value.

Different mean dopant concentrations of the compensation subsection1821, 1822, . . . in different floors may contribute in preciselyshaping the electric field in the blocking mode of the silicon carbidedevice 500. For example, shifting the electric field maximum towards thevertical center of the superjunction structure may reduce or avoidTRAPATT oscillations in the silicon carbide device.

Each current spread regions 137 may be in direct contact with one ormore compensation regions 182. The current spread regions 137 and thefirst floor F1 of the main layer 130 may have a same dopantconcentration or may form a unipolar junction.

A first load electrode 310 at the front side of the silicon carbide body100 is electrically connected with the source regions 110, the bodyregions 120, and the shielding regions 160. The gate electrode 155 maybe electrically connected to a gate metallization at the front side ofthe silicon carbide body 100. The gate metallization forms or iselectrically connected or coupled to a gate terminal.

Portions of an interlayer dielectric 210 separate the first loadelectrode 310 and the gate electrode 155 in the gate structures 150. Thefirst load electrode 310 may form or may be electrically connected withor coupled to a first load terminal, which may be an anode terminal ofan MCD or a source terminal of an MOSFET.

A second load electrode 320 forms a low-resistive ohmic contact with thecontact portion 139. The second load electrode 320 may form or may beelectrically connected with or coupled to a second load terminal, whichmay be a cathode terminal of an MCD or a drain terminal of an MOSFET.

The illustrated silicon carbide device 500 is an n-channel SiCSJ-TMOSFET, wherein the first load electrode 310 forms or iselectrically connected or coupled to a source terminal S and wherein thesecond load electrode 320 forms or is electrically connected or coupledto a drain terminal D. The silicon carbide device 500 includes aplurality of transistor cells TC and a plurality of gate structures 150,wherein the transistor cells TC are electrically connected in parallel.

In FIG. 8 the fill structure 190 includes a liner portion 194 separatinga fill portion 195 and the silicon carbide body 100. The liner portion194 may include a conductive material, for example p-doped siliconcarbide whereby this doping has to be taken into account choosing thedoping levels of the compensation layers so that the desired degree ofcharge balance is achieved. Alternatively, the liner portion 194 may bea dielectric liner. The fill portion 195 may include dielectric materialor conductive material, e.g., doped polycrystalline silicon carbide.

The silicon carbide device 500 further includes compensation adjustmentregions 185. Each compensation adjustment regions 185 is formed directlybelow and in contact with a compensation layer portion 161. Eachcompensation adjustment regions 185 is formed laterally next to and incontact with another compensation layer portion 161 or with thecompensation bottom region 189.

In FIG. 9 the fill structures 190 include a field plate 196. Adielectric portion 197 of the fill structures 190 insulates the fieldplate 196 and the silicon carbide body 100. The field plate 196 mayextend along the complete longitudinal extension of the gate structure150 and may be electrically connected to the first load electrode 310 ina cross-sectional plane parallel to the illustrated cross-section. Thefield plate 196 includes a conductive material, for example ametal-containing material, doped polycrystalline silicon or dopedpolycrystalline silicon carbide. A vertical extension of the field plate196 may be at most 200 nm, e.g., at most 60 nm. A dielectric structure198, for example thermally grown silicon oxide may separate the gateelectrode 155 and the field plate 196. The field plate 196 maycontribute in reducing the electric field strength at the bottom of thegate structure 150 and may enhance the reliability of the gatedielectric 159.

FIG. 10 illustrates a compensation structure 180 based on fillstructures 190 with stepped sidewalls 191 in combination with planargate structures 150. Two transistor cells TC may be formed within eachportion of the silicon carbide body 100 laterally between twoneighboring fill structures 190. The two transistor cells TC may beformed symmetrically with respect to a vertical symmetry plane and mayshare a common planar gate structure 150.

The planar gate structure 150 is formed above a section of the firstsurface 101 between neighboring fill structures 190. The planar gatestructure 150 includes a gate dielectric 159 and a gate electrode 155.The gate dielectric 159 may be directly formed on the first surface 101.The gate electrode 155 may be formed directly on the gate dielectric159.

Source regions 110, body regions 120 and current spread regions 137 ofthe transistor cells TC may be formed in an upper section of the firstfloor F1 of the main layer 130. The body region 120 of the lefttransistor cell TC directly adjoins a section of the first surface 101below the gate electrode 155 and may be in contact with the uppermostfirst compensation portion 181 at the left hand side. The body region120 of the right transistor cell TC directly adjoins another section ofthe first surface 101 below the gate electrode 155 and may be in contactwith the uppermost first compensation portion 181 at the right handside. The source regions 110 of the transistor cells TC are formedbetween the first surface 101 and the respective body region 120. Thecurrent spread region 137 is shared between the two transistor cells TCand directly adjoins a section of the first surface 101 directly below acentral portion of the gate electrode 155. The current spread region 137may be in contact with a compensation region 182. For example, thecurrent spread region 137 and the compensation region 182 may form aunipolar junction.

The fill structures 190 may be slightly recessed. Portions of the firstload electrode 310 may form contact structures 315 extending from theplane of the first surface 101 into the silicon carbide body 100 down tothe recessed fill structure 190. The contact structures 315 may formlateral ohmic contacts with the source regions 110 and with uppersections of the topmost compensation layer portions 181.

FIGS. 11A-11B show a silicon carbide device 500 with trench gatestructures 150 running orthogonal to the fill structures 190.

FIGS. 12A-12B show transistor cells TC based on gate structures 150 withtwo-sided channels and active first and second gate sidewalls 151, 152.Source regions 110, body regions 120, current spread regions 132 andshielding regions 160 may extend from a first gate sidewall 151 of afirst gate structure 150 to a second gate sidewall 152 of a second gatestructure 150, wherein metal source contact structures may extend fromthe first surface 101 through the source regions 110 into the bodyregions 120. Portions including the source regions 110, the body regions120 and the current spread regions 132 may alternate with shieldingregions 160 along a lateral direction parallel to the laterallongitudinal extension of the gate structures 150.

In FIGS. 3A to 12B, three floors F1 to F3 and a top layer F0 are shown.However, these are only examples. The number of floors may be smaller orlarger by using more or less process loops of masking, trench etchingand implantation steps as described above.

For illustration, various scenarios have been described with respect toa silicon carbide device. Similar techniques may be implemented insemiconductor devices based on other kinds and types of compoundsemiconductors material for the silicon carbide body, e.g., galliumnitride (GaN) or gallium arsenide (GaAs), etc.

Also for illustration, various techniques have been described withrespect to the self-alignment of larger openings in a first process maskwith reference to smaller openings in a second process mask. Similartechniques may be implemented in other kinds and types of formingprocess masks with openings that can be aligned to each other with highprecision and high reproducibility on silicon carbide substrates.

What is claimed is:
 1. A method of manufacturing a silicon carbidedevice, comprising: implanting first dopants through a larger opening ofa first process mask into a silicon carbide body, wherein the largeropening exposes a first surface section of the silicon carbide body; andforming a trench in the silicon carbide body in a second surface sectionexposed by a smaller opening in a second process mask, wherein thesecond surface section is a sub-section of the first surface section,wherein the larger opening and the smaller opening are formedself-aligned to each other, wherein at least part of the first dopantsform at least one compensation layer portion extending parallel to atrench sidewall.
 2. The method of claim 1, wherein the first dopants areimplanted prior to forming the trench, and wherein the smaller openingis formed by forming a spacer along a sidewall of the larger opening. 3.The method of claim 1, wherein forming the trench and the at least onecompensation layer portion comprises: repeating at least once animplant/etch sequence, wherein the implant/etch sequence comprisesimplanting first dopants through a larger opening and forming a trenchsection in a section exposed by a smaller opening, wherein the smalleropening is formed by forming a spacer along a sidewall of the largeropening, and wherein a width of the larger opening of the (n+1)thimplant/etch sequence is equal to or smaller than a width of the smalleropening of the n-th implant/etch sequence.
 4. The method of claim 1,further comprising: implanting further first dopants through a trenchbottom of the trench, wherein the further first dopants form acompensation bottom region extending from the trench bottom into thesilicon carbide body.
 5. The method of claim 1, wherein the firstdopants are implanted after forming the trench.
 6. The method of claim5, wherein the larger opening is formed by widening the smaller opening.7. The method of claim 5, wherein forming the trench comprises repeatingat least once an etch sequence, wherein the etch sequence comprisesforming a trench section in a section exposed by a smaller opening,wherein the smaller opening of the (n+1)th etch sequence is smaller thanthe smaller opening of the n-th etch sequence.
 8. The method of claim 7,wherein the smaller opening of the (n+1)th etch sequence is formed byforming a spacer along a sidewall of the smaller opening of the n-thetch sequence.
 9. The method of claim 7, further comprising: implantingauxiliary dopants into the silicon carbide body, wherein the auxiliarydopants and the first dopants have complementary conductivity types,wherein implanting the auxiliary dopants comprises an ion beamimplantation with the ion beam tilted with respect to a verticaldirection, and wherein the implanted auxiliary dopants form compensationadjustment regions at opposite sides of the trench sections.
 10. Themethod of claim 1, wherein the silicon carbide body comprises a mainlayer, wherein the main layer and the at least one compensation layerportion have complementary conductivity types, and wherein the trenchextends into the main layer.
 11. The method of claim 1, furthercomprising: forming a transistor cell that comprises a source region anda body region, wherein the source region and the body region form a pnjunction, and wherein the source region and the body region are formedbetween a first surface of the silicon carbide body and the at least onecompensation layer portion.
 12. The method of claim 1, furthercomprising: after forming the trench, implanting supplementary dopantsof the conductivity type of the first dopants into the silicon carbidebody, wherein implanting the supplementary dopants comprises an ion beamimplantation with the ion beam tilted with respect to a verticaldirection, wherein the implanted supplementary dopants form connectionregions, and wherein each connection region is in contact with and/oroverlaps two neighboring compensation layer portions.
 13. A siliconcarbide device, comprising: a fill structure extending from a firstlateral cross-sectional plane of a silicon carbide body to a secondlateral cross-sectional plane, the fill structure comprising at leastone stepped sidewall that includes at least two steep sidewall portionslaterally shifted to each other; and compensation layer portions formedin the silicon carbide body, wherein each compensation layer portionextends along one of the steep sidewall portions.
 14. The siliconcarbide device of claim 13, wherein the fill structure comprises twostepped sidewalls on opposite sides.
 15. The silicon carbide device ofclaim 13, further comprising: a compensation bottom region formed in thesilicon carbide body, wherein the compensation bottom region is incontact with a bottom surface of the fill structure.
 16. The siliconcarbide device of claim 13, wherein the compensation bottom region andthe compensation layer portions are structurally connected with eachother.
 17. The silicon carbide device of claim 13, wherein the fillstructure includes at least one dielectric structure.
 18. The siliconcarbide device of claim 13, further comprising: compensation regions incontact with the compensation layer portions, wherein each compensationlayer portion is laterally between the fill structure and one of thecompensation regions, and wherein the compensation layer portions andthe compensation regions form pn junctions.
 19. The silicon carbidedevice of claim 13, further comprising: an emitter region of aconductivity type of the compensation layer portions, wherein theemitter region is formed between a first surface of the silicon carbidebody and the first lateral cross-sectional plane.
 20. The siliconcarbide device of claim 13, further comprising: a compensationconnection region connecting two neighboring compensation layerportions, wherein the compensation connections regions and thecompensation layer portions have a same conductivity type.
 21. Thesilicon carbide device of claim 13, further comprising: a compensationadjustment region in contact with two neighboring compensation layerportions, wherein the compensation adjustment region and thecompensation layer portions have different conductivity types.